Such optical displays are known as the additional third brake light on passenger vehicles, where the LEDs are connected in a parallel connection of n series connections with a maximum of three to four LEDs or as a matrix circuit in a series connection of a maximum of three to four parallel connections of n LEDs of the same forward voltage class. To set the current, the LEDs are provided with series resistors, where the resistance values are selected as a function of the forward voltage class of the respective LEDs.
It would essentially be advantageous to also use LEDs for implementation of the incandescent bulbs used in the past, especially for taillights, brake lights, back-up lights, flashing indicators, etc. on automobiles. Disadvantages of incandescent bulbs include the fact that they have a poor efficiency and a limited lifetime; corresponding colors (wavelengths) must be implemented with additional filters which produce additional losses; incandescent bulbs are bulky and therefore a shallow design adapted to the shape of the vehicle is impossible; due to the limited lifetime, it is necessary to use lamp sockets that permit a simple replacement and thus also take up additional space in the vehicle; incandescent bulbs have a delayed turn-on response, which is manifested especially in braking operations; and brightness control of incandescent bulbs with direct voltage is possible only with loss resistance and thus with corresponding heating.
In comparison with these disadvantages of incandescent bulbs in the automotive area, LEDs have a long lifetime and permit space savings due to the small flat design and the possibility of the three-dimensional arrangement of the lighting elements, for example in the trunk area of a passenger vehicle. Irt addition, different colors are possible since a light spot of any color can be produced with a mixture of red, green and blue LEDs, or LEDs with different colors Due to the possibility of rapid turn on, they present an increased safety aspect especially when used as a brake light, lengthening the stopping distance for the following automobile by approximately five meters when traveling at a speed of 120 km/hr, for example, because it is possible to detect the leading car's braking action sooner. In addition, LEDs have a high shock resistance and vibration resistance as well as a lower inherent temperature. The power required to produce the same brightness is lower by a factor of 4 to 5.
Nevertheless, in implementation of LEDs, especially for brake lights and taillights, with the possible implementations available in the past there has been a high power consumption, which is converted almost completely into heat at resistors and semiconductor components (typically 3 to 5 watts). This evolution of heat in conjunction with temperatures occurring in the vehicle can lead to an unacceptably high chip temperature of more than 125.degree. C. under conventional installation conditions. Therefore, to prevent additional heat problems with the LED brake lights known in the past, the number of LEDs per light is preferably selected as an integral multiple of 3 or 4. The arrangement of resistors and/or semiconductor components on the LED circuitboard represents an additional thermal stress for the LEDs. Another problem for mass production of such lights is the different forward voltage classes of the LEDs because a mixed assembly is impossible especially with the above-mentioned matrix circuit with a series connection of a maximum of 3 to 4 parallel connections of n LEDs in the same forward voltage class. Consequently, several different forward voltage classes must be processed for each light project, which leads to an undesirable variety of variants. With the series resistors used in the past, the working point of the LEDs can be set only for one voltage value of the on-board voltage in the vehicle, so that the wide distribution of the forward voltages of an LED within one class always leads to a blurred setting of the working point in the case of a resistance circuit. Super positioning of several tolerances (reflector quality, geometric tolerances, band width of the brightness classes resistance tolerances, band width of the forward voltage classes, transmittance of the light disk and the optically effective elements) can lead on the whole to a wide scattering of the light values in mass production.
Essentially, it is possible to use LEDs for signal lights not only in the automotive area but also in all means of communication or in production shops with moving units or other warning devices. In contrast to bulbs, LEDs can be switched very fast (nsec). It is also frequently necessary to relay information, especially with all means of communication, but also in production shops. For example, it might be necessary to transmit all possible information about the vehicle and/or the mount in the workshop, at the gas station, in traffic control systems, in for parking fees, toll roads, vehicle inspections, borders, etc. with regard to automation by appropriately controlled computer systems. Invisible data transmission can also be used to control air traffic at airport runways, for example, or to direct aircraft to their proper parking positions. However, invisible transmission by means of infrared, for example, has the disadvantage that a malfunction such that the transmission link is interrupted cannot be detected without additional measurement equipment.
Therefore, the object of the present invention is to propose an optical display device and a method of operating an optical display device with which information can be transmitted visibly and invisibly at the same time.